1. Field. Field
This invention relates to chemical mechanical polishing (CMP), and more particularly to improved chemical mechanical polishing with improved reproducibility, versatility, productivity, robustness, and low cost.
2. Prior Art
CMP is uniquely capable of removing thick metal films while leaving intact features inset and surrounding dielectric films in integrated circuit processing. This process has become an enabling technology for both advanced tungsten plug and copper demanscence processes. It aims to achieve global planarity, and is as crucial as metal deposition or lithography aiming. CMP is no longer a niche application with the same fixed equipment, material, and process for all device designs, material and process selections. In particular, device miniaturization and the coming of multi-metal architectures and techniques such as the emerging copper dual damascene are seriously challenging. These challenges force CMP technology including platforms, chemistries, pads and slurries to rapidly and radically evolve and improve.
Current CMP is not perfect. It must be carefully controlled for it to be optimized. A poorly executed CMP can generate extreme metal dishing in wide structures or dielectric erosion in high-density regions of smaller features. Abrasive particles containing slurries generate scratches or gouges in the inlaid structures. If a substrate is improperly post-CMP cleaned, the slurry particles can be included in subsequent dielectric deposits and depress yield. The process also reveals and highlights preexisting defects such as seams and voids encapsulated in vias and trenches during earlier copper electroplating processes, or delamination of barrier/seed layers from surrounding dielectrics not easily detected in preceding operations. Particles trapped into underlying dielectrics, barrier and seed films will appear only after the metal that coats them is removed. Shifts in film microstructure through the thickness of the deposit may affect CMP rates, or lead to effects such as pull-out of grains causing pits in the surfaces or perimeters of the inlaid metal.
CMP technology including equipment, material and processes cannot meet the needs for metal thinning, planarization and defect elimination. There is no slurry meeting all the CMP requirements. Additional problems exist as to stability and shelf life of the slurry, lot-to-lot variability of slurry products. First-step cannot always stop at the barrier layer. Second-step polish often introduces dishing, erosion, and non-uniformity.
CMP's next challenges include:
1) Adapting to smaller device features and large wafer sizes such as 300 mm;
2) Minimizing defect formation including planarity, metal thinning, nonuniform polishing, erosion, corrosion, pits, delamination, planarization, oxide and total metal loss, scratches, ruptures, topography issues with demascene structures, excessive edge exclusion below 3 mm, too much down-force pressure during CMP especially with copper and ultralow-k dielectric materials, and other damages;
3) Improving slurry stability, uniformity, deterioration during processing, shelf life, and lot-to-lot variability, all customized to possible gel formation and agglomeration of the slurries. Definite knowledge of chemistry and particle interaction, time-sensitive chemicals like an oxidizer, consistent concentration of the delivered slurry or particle density, controlling particle size-distribution in mixed powders and excessive settling associated with certain particles or combination of particles associated with a specific liquid slurry suspension medium, are also needed. These improvements are necessary for rapid development, characterization, and optimization of a specific robust CMP equipment and process for each customer's product.
4) Minimizing copper and oxide loss in double-damascene process;
5) Tailoring and integrating equipment, material, and process to new materials such as low-k films for low cost but with minimum size and complexity, maximum productivity, endpoint control, design flexibility, improved deposition rates, versatility, reliability, and robustness; and
6) Improving slurry stability, uniformity, deterioration during processing, shelf life, and lot-to-lot variability, all customized to possible gel formation and agglomeration of the slurries. Also needed are definite knowledge of chemistry and particle interaction, time-sensitive chemicals like an oxidizer, consistent concentration of the delivered slurry or particle density, controlling particle size-distribution in mixed powders and excessive settling associated with certain particles or combination of particles associated with a specific liquid slurry suspension medium. These improvements are necessary for rapid development, characterization, and optimization of a specific robust CMP equipment and process for each customer's product.
6) Smart processing automation such as with real-time, in-situ monitoring and feed-back control, and computerized R&D for self-optimized process control;
The CMP method of surface planarization is a dominant technology in polishing glass. It also meets planarazation requirements in the <0.35 DM (micron) feature-sized multi-level devices and interconnects in the semiconductor industry. The CMP method is a preferred technology to carry out global planarization for various integrated circuits (IC). Planarized surfaces have become key to the success of advanced semiconductor devices and circuits, particularly for high-density multi-level interconnects.
In IC manufacturing, CMP involves competing requirements at various length scales—e.g., uniform removal at the wafer scale, but non-uniform removal of protruding surfaces or areas to achieve planarization at the feature scale. The process, developed so far through trial-and-error, involves a synergistic interaction of many factors: fluid flow, fluid chemistry, slurry particle materials, surface dissolution, and wafer material.
Ideally, the grinding and polishing method and equipment should provide high uniformity and selectivity, low defect levels, high removal rate, low-pressure/high-speed capability, short product development time, and low cost. Also, the solid grinding/polishing abrasive materials should always remain as sharp as possible, efficient, long-lasting, and low in initial and operating costs for rapid, reproducible grinding and polishing operations.
Grinding, polishing, or planarizing is widely used in many industries such as automotive, electronics optical, machinery, metallurgical, medical, and glass. The quality and performance of an automobile, electronic component, optical instrument, precision machinery, glass plate, metallurgical material, or biomedical samples often critically depend on the cost and quality, e.g., flatness, surface finish, and reproducibility, of the planarized material. A perfectly planarized sample is often too costly or even impossible to obtain.
Making a modern 0.25-micron CMOS IC requires 13 planarizing steps. A single major defect in any one step can result in the rejection of the entire chip lot. Even if each planarizing step has a yield of 99%, the final product yield loss from the 13 planarizing steps alone is over 12.2%. Raising yields from 99% to 99.5% in each of the 13 planarizing steps still incurs a planarizing loss of 6.3%. This is a big production and financial loss.
A planarizing machine is often used to obtain a planar, smooth outer surface on a material. The prior-art grinding and polishing machine often comprises a rotating wheel for mounting the material thereon. A colloidal liquid or liquid abrasive suspension is provided to wet the wheel and to hold/mount the material against the rotating wheel. The planarizing liquid suspension slurry comprises a liquid suspension medium and a plurality of solid abrasive particles suspended therein. The liquid suspension is fed onto the wheel to chemically and mechanically grind and polish off surface layers of the mounted material.
Both manual and automatic planarizing machines have been known in the art for quite some time. But these machines are not satisfactory in many respects. The liquid suspension is costly but is not reproducible; has short shelf lives; deteriorates in performance during use, transit, or even storage; and does not reliably produce quality product results. The solid abrasive particles wear out rapidly degrading the planarizing results. The solid abrasive particles also often agglomerate or break up into smaller pieces. Changes in particle size, e.g., over 10 to 20% over the average size, alone, lead to loss of control of the desired surface finish. A large size distribution of the solid abrasive particles produces a wide variety of surface finishes of differing smoothness and qualities, hampering product yield and reproducibility.
The hard, sharp, and brittle working edges and points on the solid abrasive particles are easily damaged, producing products of variable quality even during the same planarizing run. Damaged or worn-out particles always give inferior results. The planarizing process is then inefficient, costly and nonreproducible.
To overcome the foregoing and other difficulties, the general object of this invention is to protect solid abrasive particles and contact-sensitive parts from damage during their preparation, use, transit, and storage;
Another object of the invention is to provide an improved planarizing liquid slurry that is not only highly effective but longer lasting, and produces high-quality products;
Yet another object of this invention is to minimize damages on the working quality of a planarizing liquid suspension by making the solid abrasive particles practically forever sharp prior to use;
It is another object of the invention is to provide improved planarized surfaces finishes, rapidly and at low cost;
A further object is to greatly improve the material use efficiency of the solid abrasive particles in the planarizing operations.
Another object of this invention is to provide improved CMP methods with enhanced stability, reproducibility, versatility, productivity, robustness, product qualities, and low cost;
Yet another object of the invention is to achieve minimized defects formation, lot-to-lot variability, mixed abrasive particles settling, and deterioration of slurry performance with mixed solid abrasive particles; and
A further object of the invention is to provide completely computer-automated self-optimizing CMP operations.